Almost simultaneously the contents of the gas spheres began to have their effect. Man after man of those who remained, for several had fled, staggered and fell, while Jack and the captain retreated up the stairway. They lost no time in reaching the door at the head of the stairs and shutting it to keep out the fumes. They were none too soon. The gas had already affected them, and their heads throbbed and their eyelids felt leaden. In the corner of the room was a big earthen pitcher of water. The Professor threw the contents of this over his son and Captain Andrews, and though still heavy from the effects of the gas, the shock revived them wonderfully. “What now?” asked the Professor, after Jack and Captain Andrews had “come back to life” a little. “Wait till the fumes of the gas have evaporated through the open door downstairs, and then make a dash for freedom,” said Captain Andrews. “How long will it be before the air is good to breathe?” inquired Mr. Jesson. “About fifteen minutes,” said the Professor; “the gas is of a very volatile nature, and the fumes will soon clear off. It will be an hour or so at least, however, before the negroes recover.” “I would suggest, then, that Jack gives us a more detailed account of what occurred after he left Lone Island,” said Mr. Jesson. Falling in with this idea, they seated themselves about the lad, who at once plunged into the details of the narrative, which, as may be imagined, proved of engrossing interest to all who heard him. He was interrupted several times by questions and requests for information concerning the operation of the aero-auto, and the relation of his story took longer than had been anticipated. However, even in their critical situation, no one wanted to miss a word of it. “And so the three gems are safe?” said Professor Chadwick, with a sigh of relief, as the lad concluded. “Yes. They are at this moment in the Flying Road Racer’s locker, in charge of Tom and Ned,” was the reply. As Jack spoke they all, by mutual consent, rose and made for the door. “I shall be glad to get to the air,” remarked Professor Chadwick. “Yes; it is insufferably hot in here,” agreed Mr. Jesson. “I had not noticed the heat so much while Jack was talking; but now,—phew! It’s like a furnace.” As he spoke. Jack flung the door open. The next instant he staggered back, the hot blood in his veins frozen with horror. A rush of air, hot and arid as a blast from a coke oven, struck him in the face. A great puff of smoke followed. The room below was a vast furnace of red flame. In falling, one of the negro’s lanterns had overturned and rolled against the bales of dried hemp. All the time they had been talking the fire had been waxing more and more furious. By this time the lower part of the stairway was in flames, and, as Jack held the door open, a tongue of fire, sucked upward by the draft, shot hungrily toward him.